Optoelectronic modules, such as optoelectronic transceivers, are increasingly used in electronic and optoelectronic communication. Optoelectronic modules generally include an outer housing or casing that at least partially encloses one or more transmitters and/or receivers as well as one or more printed circuit boards (PCB) with circuitry related to the transmitters/receivers, such as driving and amplifying circuitry. Electrical data signals generally pass through this circuitry as they pass between the transmitter/receiver and a host device in which the optoelectronic module is positioned.
Known optoelectronic module assemblies must make compromises between optical connections, electrical connections, mechanical connections, and thermal management due to design limitations imposed by the assembly technologies. For example, increasing the frequency of the transmitted or received data signal permits an increased rate of data communication via the optoelectronic module. However, increasing data signal frequencies may present a number of difficulties in designing optoelectronic modules, in particular, proper thermal management.
An example of a known optoelectronic module is the Quad Small Form-Factor Pluggable (QSFP) transceiver module sold by TE Connectivity under the name “QSFP28 Transceiver”. A schematic longitudinal cross-section of this transceiver module 200 is shown in FIGS. 1 and 2. FIG. 3 is a block diagram of the QSFP transceiver 200.
The transceiver module comprises an optical engine (OE) 202 containing optical components such as vertical-cavity surface-emitting lasers (VCSELs) and photodiodes as well as electronic components for simultaneously transmitting and receiving signals between the optical and the electrical side. From the optical side, an optical ferrule (not shown in the Figure) can be connected to a fiber optic connector 204. The fiber optic connector 204 is for instance formed as a standardized so-called mechanical transfer (MT) connector. An internal fiber pigtail 206 connects the fiber optic connector 204 to the optical engine 202. An optical chip connector 208 contacts the optical engine 202.
For contacting the electrical side, the transceiver module 200 comprises a rigid edge connector 210 for contacting an electrical connector (not shown in the Figure). The edge connector 210 is an integral part of a printed circuit board (PCB) 212 which carries the OE 202.
The transceiver module 200 further comprises a casing formed by two walls 214, 216. The upper wall 214 is formed to be thermally contacted by an external heat sink 218. The heat sink 218 is a part of a cage assembly which is not shown in the Figure. A thermal bridge 220 forming part of a thermal interface conducts heat generated by the optical engine 202 towards the casing. A compressible thermal interface material, in particular a gap pad 222 connects the thermal bridge 220 with the lower wall 216 of the casing. A sealing and thermally conductive casting compound 224 fills the gap between the thermal bridge 220 and the heat generating components of the OE 202.
The position and shape of the electrical interface formed by the edge connector 210 is defined by the standard SFF-8661. As a consequence, there is not enough space for the optical engine 202 and the optical chip connector 208 to face the casing's lower shell 216, which means that the thermal interface must be disposed to interface to the casing's lower shell 216. Having the thermal interface (including the thermal bridge) arranged at the lower shell 216 results in a long heat dissipation path since the outer heat sink 218 is attached to the casing's top shell 214. The result is a higher working temperature, which influences VCSEL life time. Furthermore, since the PCB 212 has to be mechanically floating with respect to the casing, the thermal interface has to be compliant, which further decreases the thermal performance. A certain force has to be applied to the thermal interface to keep it intact, which applies mechanical stress to the solder electrical interface between the OE 202 and the PCB 212. Additionally, the predetermined position of the thermal interface results in high requirements on the length of the internal fiber pigtail 206; otherwise there will be too high mechanical stress on the optical connection to the OE 202.
In a known optoelectronic module design, the thermal, optical, mechanical, and electrical connections are tightly integrated, and optimization of one connection type interferes with the others, causing a non-optimal overall performance.